Semiconductor and similar micro-scale devices are typically manufactured on a substrate or wafer. Metal or other conductive material is plated onto features of the wafer, such as trenches and vias, to form electrical components and connections. Vacuum pre-wet is a pre-plating step used to increase plating quality, especially with features having high aspect ratios. Pre-wetting works by removing gas from the features, and filling the features with a pre-plating solution. The pre-plating solution is typically de-ionized (DI) water, with or without dilute compounds such as surfactants or acids.
By fully wetting features before the wafer enters the plating solution, metal ions in the plating solution can better diffuse into the water and fully fill the feature when plating begins. A common failure of un-wetted features is that the metal ions in the plating solution cannot reach the bottom of the feature due to a bubble of gas trapped in the feature. The trapped gas bubble tends to cause the plated metal to pinch off, leaving a void at the bottom of the feature, which results in a defect, such as an unconnected circuit line.
In a new generation of wafer electroplating machines, a wafer is clamped in a plating chuck upon entry into the machine, as described in U.S. Pat. No. 9,399,827 B2. The wafer remains in the chuck during most or all process steps within the machine, presenting engineering challenges in pre-wetting the chucked wafer. Accordingly, new pre-wetting methods and apparatus are needed.